1844.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



149 



Seed wheat grown in sand and water, in three months, increased as fol- 

 lows : — 



But the quantity of carbon thus abstracted from the air being so enormous, 

 and the carbonic acid being present in it in so small a quantity, the question 

 arises, is the air competent to supply such a demand? To ascertain its pro- 

 bability, a few calculations are required, the data for which are well esta- 

 blished. The average weight of a crop per acre is about IJ ton, and as on 

 the average one-third of the weight of a plant is c.irbon, the total carbon in 

 the crop may be reckoned as about 10 cwt. per acre. The weight of the air is 

 about 151b. per square inch, and taking the weight of the carbonic acid 

 present as 3 in 1000, and 63grs. of carbonic>cidIto contain 17 grs. of carbon, 

 it will be found that the air on each acre contains about seven tons of carbon, 

 and therefore, if the whole earth were cultivated, it could only support vege- 

 tation for 14 years. But as no proof exists that the quantity of carbonic 

 acid in^the air is lessening, and as it is being removed so enormously by vege- 

 tation, whence can come Ihe supply which maintains the equilibrium. There 

 are at least three sources that can be pointed to as supplying vast quantities 

 of carbonic acid, viz., animal respiration, volcanoes, and combustion of fuel. 



1. After respiration, the quantity of carbonic acid present in the air, will be 

 found to have increased a hundredfold, it forming one-filth of the expired air. 

 It will not then support either life or combustion. Passed through lime water 

 it renders it turbid, from the formation of carbonate of lime. It is calculated 

 that the carbonic acid exhaled from the lungs in 24 hours contains from 

 5 to 8 oz. of carbon, or from 100 to 160 lb. in the year, the difference de- 

 pending upon the amount of exercise taken. ' With increased exercise more 

 carbon is consumed in the system, and more beat produced, exactly analo- 

 gous to the consumption of carbon in a charcoal fire, carbon when being 

 oxidised always evolving heat, whether it takes place quickly or slowly. 

 Animals, such as horses and cows, would, from their bidk, be expected to ex- 

 hale at least twice as much as man, but it has been shown by Boussingault, 

 that they exhale very little more than man. The inhabitants of Great 

 Britain being taken at 20 millions, and supposing that other animals expire 

 about the same quantity of carbon, it will be found to amount to about 

 two million tons, or sufficient for about four millions of acres of cultivated 

 land. 



2. Volcanoes, both active and extinct, are continually pouring into the air 

 torrents of carbonic acid. From one in the neighbourhood of Coblentz, it is 

 reckoned that 90,0001b. of carbonic acid are dally evolved. 



3. The combustion of 20 millions of tons of coal, which is the annual con- 

 sumption of Great Britain, adds to the air 14 millions of tons of carbon, 

 and as each acre of vegetation is reckoned to require half a ton, this alone 

 is sufficient for 28 millions of acres, or nearly seven-eighths of the arable 

 land, as it is considered that there are about 34 millions of acres in culti- 

 vation. 



By such means as these, then, is the carbonic acid restored to the atmos- 

 phere as fast as it is abstracted by plants, and thus the balance is maintained. 



With regard to the ammonia. This is always present in the air, and is 

 carried down in some quantity by rain. It is considered to be the source 

 ■whence the plant derives its nitrogen, and not from the air. When its con- 

 stituents, nitrogen and hydrogen, are mixed together, they do not combine, 

 nor can they be made to combine directly, but it is formed invariably during 

 the decomposition of substances containing these two gases. If horn sbavinf,s 

 or other animal matter are heated, ammonia is evolved, and it is even given 

 off during the burning of a cigar and the distillation of coal, thus having 

 both an animal and vegetable origin. It will neither burn nor support com- 

 bustion, is rapidly absorbed by water, and being an alkali, renders turmeric 

 paper brown, and restores the hlue to liquids that have been reddened by 

 acids. It may bo made to combine with excess of oxygen and then is con- 

 verted into nitric acid and water; in this manner nitrate of ammonia is 

 formed during lightning, and Faraday considers it likely that the points of 

 trees, being silent dischargers of the electricity of the earth, in this way 



1 According to this calculutiou, the carbon of the daily food, amounting to about 1 lb., 

 19 one b.ilf returned to the air as carljonic acid. 



contribute to the formation of nitrates in the air. Rain water, evaporated 

 along with an acid to prevent the ammonia from volatilizing, vill be found 

 to contain nitric acid, sulpliuric acid, and ammonia, thus supplying to the 

 plant its necessary ingredients. The quantity of nitrogen in plants varies, 

 but is always present, even when the soil contains none, and therefore in 

 such cases must come wholly from the air, as must also be the case with wild 

 plants and trees. Boussingault, to whom science is much indebted for the 

 laborious manner in which he has investigated these subjects, testing theories 

 by practice on a large scale, found that in five years' rotation of crops the 

 nitrogen as well as the carbon, was present in greater quantities than the soil 

 could possibly yield. A crop of .lerusalem artichokes, which gave 23,300 lb. 

 to the acre, contained 381b. more nitmgen than the soil could have <'iven. 



The quantity of nitrogen that various crops contain, and its proportion to 

 the carbon and other constituents, is well seen in the followin" table : 



Although the quantity of ammonia contained in rain water is very small, 

 one pound containing but a quarter of a grain, yet when the total annual 

 quantity of rain that falls is considered, it will be found to yield a consider, 

 able amount of nitrogen to the plant. The average number of inches of rain 

 that falls in Great Britain is about 22 inches and four-tenths, which will give 

 a weight of 1171b. to the square foot, or 5,096,5001b. per acre, ami at a 

 quarter of a grain of ammonia per pound, is equal to about 1201b. of nitro- 

 gen. Nitrogenous substances are useful to plants, not only as forming part 

 of their substance, but as acting as a stimulant, enabling it to draw the same 

 substance in greater quantity from other sources ; in a similar manner sail, 

 muriate of lime, and other substances, arefsupposed to act, as by their 

 agency the gluten or nitrogenous part of wheat is always increased. 



It has thus been [shown that plants require two classes of food, organic 

 and inorganic. The inorganic must be rendered soluble, and must be the 

 same as are found in the ashes of plants, which are separated from the other 

 parts by burning. The organic food, composed of carbon, oxygen, nitrogen, 

 and hydrogen, must be presented to it in the form of water, carbonic acid, 

 and ammonia. Having thus then considered the constituents of wliicli all 

 other parts are built up, it remains to examine the subject under three 

 heads : — 



1st. The products elaborated by the functions of the plant, known as the 

 proximate elements. 



2nd. The mode in which, by its vital force, it eliminates them.'; 



3rd. The mechanical conditions of the soil requisite to enable the plant to 

 carry on these operations in the greatest health and vigour. 



Ellis's Improved lum-TaUe. — The objection to placing turn-tables of the 

 ordinary construction on the main line of a railway, is, that, by the nature of 

 their construction, they are rapidly destroyed, by the frequent passage of 

 heavy trains over them, besides the injury done to the carriages, and the un- 

 pleasant motion and uoise. Mr. Ellis has constructed a turn-table, which, 

 when not in use, rests firmly on the curb, and thus allows the train to pass 

 rapidly over it without injury. The iron pintle of the table on which it turns 

 being kept well oiled, works with a loose collar round it in a vertical iron 

 case ; which case is supported and kept in its central position by two cross 

 arms of cast iron, at right angles to each other, and attached to the curb. 

 The lower end of the pintle passes through the bottom of the case, below 

 which is a stirrup attaclied to a cross lever passing at one end through a 

 chase in the circular masonry, or brickwork, supporting the table : attached 

 to the external end of the long lever, is a second lever, working in a vertical 

 direction, and connected with a third, or handle lever, by which the table is 

 put in motion or fixed, as required. 



FotjNT.MN ExTRAORDiNARv.— The great fountain now in progress at Chats- 

 worth, is expected to jilay to a height of upwards of I'OU feet. The fountain that l)lays 

 the highest jet of any fountain in the world at present is in Germany, but the proposed 

 fountain at Chatswortfa is expected to surpass it in height about I'D ft. — Derby Wercury. 



